Breast cancer is the most common tumor type and the leading cause of cancer-related death in women (Jemal et al., CA Cancer J Clin., 2011). Considerable progress has been made in terms of breast cancer diagnosis and treatment in the last years.
After surgical removal of the primary tumor, breast cancer patients are frequently treated with radiotherapy, hormone therapy and cytotoxic chemotherapy to reduce the risk of recurrence. Today, anthracycline and taxane-based treatment strategies are commonly used in clinical routine, since these regimens have been shown to be superior compared to other standard chemotherapies.
Several large clinical trials demonstrated that the addition of taxanes to anthracycline-based treatment strategies results in an improved clinical outcome (Martin et al., NEJM, 2005, Gianni, J C O, 2009). Although, taxanes are among the most active agents, the absolute benefit of taxane-based treatment is modest (3-5%) and has to be balanced according to serious side-effects.
To reduce the number of patients suffering from side effects without a clear benefit of the therapy regimen, there is a great need for novel predictive tests to identify a group of patients that can be safely treated with conventional chemotherapy and a subgroup that has a significant benefit of taxane-based treatment.
Considerable efforts have been made to identify biomarkers that allow a prediction of a specific treatment while minimizing the risk of unnecessary side effects. Ki67—a well-known cell proliferation marker—has been described to predict the benefit from adjuvant taxane-based treatment in the PACS01 trial (Penault-Llorca, J C O, 2008). However, neither the association between Ki67 index and treatment effect nor any other clinicopathological parameter or biomarker predictive for the efficiency of taxanes has been validated so far.
The most challenging treatment decision in this context concerns ER+/HER2-breast cancer patients, for which classical clinical factors like grading, tumor size or lymph node involvement do not provide a clear answer to the question whether to use chemotherapy or not and what type of treatment therapy is appropriate for the individual patient.